Drunk people aren't as easy to buy gifts for as you might think. It's true that everything they need to keep themselves entertained comes in a nice little bottle, but on the other hand they could probably really use something practical to compliment their drunkenness—something they can appreciate even when they are sober and something you can appreciate even when they are drunk. But what do you get for a person who likely won't remember that you bought them a gift? The best path to go down is the one that will make you both happy. Whatever you buy should triple as a durable necessity for when your drunk friend is too drunk, something that will minimize your involvement in their late-night shenanigans, and something that will still seem like a useful/fun gift if they open it sober.